Numerical Simulation Of Structural Responses Of A Ship Suffering Underwater Explosion Loads

The shock resistance capability of naval ships is one of the most concerned subjects for those countries with powerful navies. In face of this circumstance and the current status of shockproof research in our country, this thesis studies the structural responses of a navy ship and its shaft suffering underwater explosion loads by numerical simulation according to a real demand, which will be helpful to the shockproof design of navy vessels. Six chapters are included and organized as follows.In Chapter 1, introduced at first is the background of this research and further reviewed is the literature about underwater explosion loads as well as the shockproof research. In Chapter 2, the underwater explosion and bubble loads are expatiated. Also discussed are the cavitation and the mechanism of local cavitation and the fluid-structure interaction, which provides a theoretical base for the analysis of explosion responses.In Chapter 3, a numerical model including the whole hull structure, the equipment pedestals and the structures such as the mast, the ship fin and the ship nose, is established. According to the weight distribution of the whole ship, the mass elements are set up to make the weight distribution of the model the same as the real ship. Taking into account the model scale, simulation precision as well as efficiency, this thesis builds the fluid model with a reasonable ratio of the ship and the fluid domain and meshes it appropriately. Modal analysis shows that the model rigidity coincides almost with the real one, which offers a valid model of the ship structure and fluid for further analysis.In Chapter 4, the structural responses of a ship suffering underwater explosion loads are simulated with FEA, combining the coupled fluid-solid interaction and cavitation. The analysis indicates that the maximum velocity of the ship bottom decays exponentially as the distance to the charge increases, and as the height of the ship raises, the acceleration responses decrease while the velocity responses are in opposite. When the charge of explosion is large and close to the structure, the vertical thin shells of the ship, such as ribs and dissepiments close to the charge, start to have plastic deformation, while the rigid structures, for example, the chief and side keels, have no plastic deformation due to the larger thickness. The simulation of equipment pedestals as well as the ship fin provides shock spectra for the shockproof design of equipments in many situations.In Chapter 5, shock responses of the shaft based on the ship environment and on the hypothesis that the input at each bearing is identical are analyzed, respectively. The results from the first method show that shaft acceleration responses increase as the distance to the charge decreases, and the responses at locations between bearings are higher than those at bearings. Changes of responses along the shaft are gently, with the largest ratio being 8.47. However, the results from the second method show that the responses at bearings are very close, and those between bearings change sinusoidally and drastically, with the largest ratio being 44. Though the latter method uses less time and does not need a complicated ship model, the former can yield responses more coincident with those of the ship suffering underwater explosion loads, which proves it more reasonable.In Chapter 6, conclusions of this thesis are summarized and further work is suggested.